Computer power supply

ABSTRACT

An object of the present invention is to provide a computer power supply in which, by improving the circuit itself, internal heat loss can be reduced, thereby greatly improving efficiency. A partial resonance circuit  8  is constituted by a primary side winding N 1  of a high frequency transformer  3 , a resonance condenser  7 , and two switching elements Q 1 , Q 2 , a secondary side output circuit  4  for driving a load is connected to a secondary side of the high frequency transformer  3  via a winding, and a reverse converter  11  for driving and halting the first switching element and second switching element by causing the respective phases thereof to differ on the basis of a driving signal is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a computer power supply for drivingvarious loads using, for example, a DC output following rectification byan AC side power circuit of an AC voltage from a commercial AC powersupply or a DC voltage from a DC power supply such as a battery orsecondary battery.

2. Description of the Related Art

When a switching power supply with a high output capacitance (200 to 300W) is provided in a 1 U (height 44 mm units) size as the computer powersupply described above, a large number of cooling fans are usedconventionally in order to extract an output capacitance of 210 W ormore due to the small size, and in so doing decreases in efficiency dueto internal heat loss can be avoided. In many cases, however, efficiencyof only 65% to 68% or thereabouts can be achieved, and moreover, powerconsumption increases as the number of cooling fans rises. As a result,considerable increases in efficiency cannot be achieved, andimprovements are urgently desired.

A device which is constituted such that the internal temperature ismaintained at a constant level at all times by modifying the dischargerate of the cooling fan in accordance with the amount of generated heat,which varies according to the load current, has also been proposed (seeJapanese Unexamined Patent Application Publication 7-231058 (FIG. 1),for example).

In the aforementioned publication, the discharge rate of the cooling fanis reduced when the load current is small, and thus efficiency can beimproved slightly in comparison with a device in which a large number ofcooling fans are all driven. However, this device does not provide anultimate solution.

SUMMARY OF THE INVENTION

The present invention has been designed in consideration of thesituation described above, and it is an object thereof to provide acomputer power supply in which efficiency is improved greatly byimproving the circuit itself such that internal heat loss itself isreduced.

In order to solve the aforementioned problem, a computer power supply ofthe present invention is such that a first switching element and asecond switching element operating with a DC voltage as an input aredisposed on the primary side of a high-frequency transformer in a stateof differing polarities, the first switching element is connected to oneend of a primary side winding of the high-frequency transformer, and thesecond switching element is connected to the same end of the primaryside winding as the connection side of the first switching element via aresonance condenser, whereby the primary side winding, resonancecondenser, and two switching elements constitute a partial resonancecircuit. A secondary side output circuit for driving a load is connectedto the secondary side of the high-frequency transformer via a winding, afirst driving circuit and a second driving circuit having a delayelement are provided for driving and halting the first switching elementand second switching element on the basis of a driving signal by causingthe respective phases thereof to differ, and a reverse converter isprovided for supplying to the input portion of one of the drivingcircuits insulation from the other driving circuit and a reverse inputvoltage.

By using the partial resonance circuit and reverse converter, drops inthe flyback voltage generated when a forward converter is used can beavoided, and by providing the driving circuit with a delay element, whenone of the two switching elements is not driven (OFF) and the otherswitching element is driven (ON), or conversely when one of theswitching elements is driven (ON) and the other switching element is notdriven (OFF), the part at which operation of the two switching elementsoverlaps can be reduced to the lowest level possible.

By constructing an arrangement wherein the reverse converter is disposedabout an iron core such that the primary side winding and secondary sidewinding have differing polarities, both an insulation effect and areverse output effect can be obtained.

By providing a magnetic amplifier having a dead angle in the secondaryside output circuit or providing a magnetic snubber in a synchronousrectifier circuit, the outflow of the secondary side current can bedelayed.

By connecting the primary side winding end and an earth side end of atleast one of the switching elements in series via two condensers havingdiffering capacities and connecting a diode in parallel to the condenserwith the smaller capacity, switching loss when the switching elementsare not driven (OFF) can be reduced.

Two auxiliary windings, which are different to an output windingprovided on the secondary side of the high-frequency transformer, aredisposed on the secondary side, two synchronous rectifier drivingcircuits for transferring the output from the primary side with littleloss are connected to the two auxiliary windings respectively in a stateof differing polarities, and a switching element for the two synchronousrectifier driving circuits, which is provided with an ON-OFF signalsynchronously with the secondary voltage of the high-frequencytransformer, is provided.

An ON-OFF signal is provided to each switching element of the switchingelements for the two synchronous rectifier driving circuitssynchronously with the secondary voltage of the high-frequencytransformer. A secondary waveform from the reverse converter of thedriving circuit of the first phase of the present invention provides OFFsynchronicity with a sufficient voltage produced by the flyback energy,and thus in comparison with high-frequency diode rectification, thesecondary voltage of the high-frequency transformer has power loss onlyof the ON resistor of the switching element. Thus high efficiency can berealized.

Two resistors for determining the ON periods of the first switchingelement and second switching element are connected to a PWM controlcircuit for outputting the driving signal so as to be parallel when acomparator for controlling the ON periods of the first switching elementand second switching element is ON.

By means of such a constitution, when an input voltage is inputted or anON signal from a remote controller is inputted, a soft start can becaused and the switching element does not attempt to rise in a fullyopen state (rise rapidly during a short ON period), and thus transientssuch as an overshoot or undershoot can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic electric circuit diagram of a computer powersupply;

FIG. 2 is a view illustrating current flow when a first FET is ON and asecond FET is OFF;

FIG. 3 is a view illustrating current flow when the first FET and secondFET are both OFF;

FIG. 4 is a view illustrating current flow when the first FET is OFF andthe second FET is ON;

FIG. 5 is a view showing a primary side switching circuit of thecomputer power supply;

FIG. 6 is a view illustrating a secondary side current flow when thefirst FET is ON and a fourth FET is ON;

FIG. 7 is a view illustrating the secondary side current flow when thefirst FET is OFF and a fifth FET and sixth FET are both ON; and

FIG. 8 is a time chart showing the elapse of time of a voltage waveformand current waveform in a specified location on the primary side and avoltage waveform on the secondary side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a computer power supply which is typically provided with acircuit for converting, for example, an AC voltage from a commercial ACpower supply into a DC voltage by means of rectification and uses the DCvoltage from the circuit. To facilitate description, however, theexample shown in FIG. 1 comprises a battery 1 for generating a DCvoltage, although the present invention is not limited thereto. Thesecondary side output shown in FIG. 1 is capable of extracting threeoutput voltages of +12V, +5V, and +3.3V, but the number of outputs andthe magnitudes of the output voltages may be set at will.

The computer power supply is constituted by a primary side switchingcircuit 2 which operates using the DC voltage of the battery 1 as aninput, and a secondary side output circuit 4 provided on the secondaryside of a high frequency transformer 3 for driving various devices of acomputer using the output from the switching circuit 2 via the highfrequency transformer 3.

The primary side switching circuit 2 connects a first FET (field effecttransistor) Q1 serving as a first switching element and a second FET(field effect transistor) Q2 serving as a second switching element via aresonance condenser 7 to the negative pole side of a primary winding N1provided on the primary side of the high frequency transformer 3 in astate of opposite polarities. More specifically, the drain side of thefirst FET Q1 and the cathode side of the second FET Q2 are connectedrespectively, a first driving circuit 5 having a delay element (a delaycircuit, for example) which drives the first FET Q1 on the basis of adriving signal is connected between the gate and cathode of the FET Q1,and a second driving circuit 6 having a delay element (a delay circuit,for example) which drives the second FET Q2 on the basis of a drivingsignal is connected between the gate and cathode of the second FET Q2.The primary winding N1, the resonance condenser 7, and the two FETs Q1,Q2 constitute a partial resonance circuit 8 which is resonated only whenthe FETs Q1, Q2 are both OFF. Note that parasitic diodes 9, 10 arecomprised in the interior of the FETs Q1, Q2 respectively.

A reverse converter 11 is provided between the first driving circuit 5and second driving circuit 6 for giving insulation between the twodriving circuits 5, 6 and supplying a reverse output voltage to thesecond driving circuit 6.

The reverse converter 11 is constituted such that a primary side winding11B and a secondary side winding 11A are disposed about an iron core 11Cin a state of opposite polarities, or in other words if the right sideof the primary side winding 11B in the drawing is set as a negativepole, the right side of the secondary side winding 11A becomes apositive pole, and thus a flyback voltage from the primary side winding11B when a third FET Q3 is OFF can be transferred to the secondary sidewinding 11A in a reversed state. The third FET Q3 is provided as a thirdswitching element for driving the reverse converter 11. The referencesymbol 14 in FIG. 1 is a third driving circuit which is connected to thegate of the third FET Q3 to drive the third FET Q3 on the basis of adriving signal from a PWM control circuit 24 to be described below.

By connecting the primary side winding N1 end (drain side) and the earth(cathode) end of the first FET Q1 in series via two condensers 12, 13with differing capacitance, and connecting the condenser 12 with thesmaller capacitance in parallel with a diode 14, switching loss when thefirst FET Q1 is OFF can be reduced.

To describe the operations of the first FET Q1 and second FET Q2, whenthe first FET Q1 is switched ON (and the second FET Q2 with a differentpolarity is OFF) by a driving signal from the PWM control circuit to bedescribed below which is outputted from the first driving circuit 5, acurrent I_(1A) flows as shown in FIG. 2. Next, when the first FET Q1 isswitched OFF, a current I_(1B) flows along the parasitic diode 10 asshown in FIG. 3 in order to charge the resonance condenser 7. Byproviding the second FET Q2 such that the excitation of thehigh-frequency transformer 3 is reset by causing a flybackcounter-electromotive force of the high-frequency transformer 3 to flowinto the resonance condenser 7, switching loss when the first FET Q1 isturned OFF can be reduced. In other words, when the second FET Q2 is notprovided, the flyback voltage of the high frequency transformer 3 risesrapidly when the first FET Q1 is OFF, causing a large amount of turn-offloss which is generated during a cross when the drain current flowinginto the first FET Q1 is turned OFF. When charging of the resonancecondenser 7 is complete, the second FET Q2 switches ON (the first FET Q1remains OFF), and the energy stored in the resonance condenser 7 isdischarged such that a current I_(1C) flows as shown in FIG. 4. Whendischarge is complete, the first FET Q1 turns ON again, and theoperation described above is repeated. When the first FET Q1 switchesON, if the second FET Q2 is not provided, falling of the voltage betweenthe drain and source of the first FET Q1 is delayed, and turn-on lossincreases as the ON current of the first FET Q1 rises.

The secondary side output circuit 4 comprises four windings N2, N3, N4,and N5 disposed on the secondary side of the high frequency transformer3. The positive pole side of the winding N3 positioned on the upper sideof the drawing is connected via a magnetic amplifier 19A to a high-speedrectifier diode 15 serving as a secondary side rectifying element, andthus a +12V voltage can be obtained. However, a FET or the like may beused in the flywheel side diode in order to suppress power loss.Further, by connecting two synchronous rectifier driving circuits 16, 17for transferring the output from the primary side with little loss tothe winding N2 positioned third from top in a state in which thepolarities of the two auxiliary windings N4, N5 positioned second andfourth from top are different from one another, or in other words byconnecting the first synchronous rectifier driving circuit 16 on theupper side to the positive pole side of the winding N4, connecting thesecond synchronous rectifier driving circuit 17 on the lower side to thenegative pole side of the winding N5, and providing a fourth FET Q4serving as a synchronous rectifier side switching element and a fifthFET Q5 and sixth FET Q6 serving as flywheel side switching elements,which switch ON and OFF on the basis of an output signal from the twosynchronous rectifier driving circuits 16, 17, a synchronous rectifiercircuit is provided. When the fourth FET Q4 switches ON while the firstFET Q1 is ON, +3.3V and +5V are outputted, and when the flywheel sidefifth FET Q5 and sixth FET Q6 switch ON while the first FET Q1 is OFF,the three FETs Q4, Q5, and Q6 are respectively connected so as to output+3.3V and +5V by the counter-electromotive force of choke coils 18C,18B. The reference symbol 30 in FIG. 1 is a magnetic amplifier 19Acontrolling circuit for controlling a +12V output to a constant voltage,and the reference symbol 20 is a magnetic amplifier 19B controllingcircuit for controlling the +3.3V output to a constant voltage. Thereference symbol 21 shown in FIG. 1 is a current transformer fordetecting an overcurrent which constitutes an overcurrent protectioncircuit not shown in the drawing. As described above, a +12V output isobtained by means of rectification using the high-speed rectifier diode15, and thus power loss due to the VF (forward threshold voltage) of theflywheel side diode (high-speed rectifier diode) 15 increases. Hence, byconnecting a FET which is driven by the synchronous rectifier drivingcircuit 17 similarly to the fifth and sixth FETs Q5, Q6 in place of theflywheel side diode (high-speed rectifier diode) 15 which operates in asimilar manner to the fifth and sixth FETs Q5, Q6, power loss can besuppressed to a low level.

To describe operations of the fourth FET Q4, fifth FET Q5, and sixth FETQ6 using FIG. 6, first, the first FET Q1 is switched ON and the currentI_(1A) shown in the drawing flows into the primary side winding N1,whereby the output of the first synchronous rectifier driving circuit 16is received such that the fourth FET Q4 switches ON. As a result, acurrent I₁ flows so as to generate a +5V output and a current I₂ flowsso as to generate a +3.3V output, as shown in FIG. 6.

When the first FET Q1 is switched OFF, the energy which was accumulatedin the smoothing choke coils 18B, 18C while the first FET Q1 was ON isdischarged as a counter-electromotive force, and thus the output of thesecond synchronous rectifier driving circuit 17 is received to switchthe fifth FET Q5 and sixth FET Q6 ON. As a result, a current I₃ flows soas to generate a +5V output and a current I₄ flows so as to generate a+3.3V output, as shown in FIG. 7.

As shown in FIG. 1, the magnetic amplifiers 19A, 19B, each having a deadangle, are connected to the two windings N2, N3 respectively, and thusthe dead angle (also known as a conduction angle) in the T1 region inFIG. 8 is used to delay outflow of the secondary side current such thatloss of the ZVS (zero voltage switching) function can be prevented. Notethat by using a magnetic snubber 28 in series with the +5V rectifier FETQ4 in which a magnetic amplifier is not inserted (not switched ON),similar effects to a case in which the magnetic amplifier 19 is providedcan be attained. Note that in the case of a multi-output, the twocomponents can be used in conjunction. The reference symbol 29 in FIG. 1is a parasitic diode comprised in the interior of the fourth FET Q4.

As shown in FIG. 1, the PWM control circuit 24 is provided forgenerating a driving signal by inputting the output of a +5V constantvoltage control circuit 22 via a photocoupler 23, and two resistors R1,R2 for determining the amount of time the first FET Q1 and second FET Q2are to be ON are connected to the PWM control circuit 24 so as to beparallel when a comparator 25 for controlling the ON times of the firstFET Q1 and second FET Q2 is ON. A remote signal is inputted into thereference voltage input side of the comparator 25 via a photocoupler 26.

Typically, when an input voltage is inputted or an ON signal from aremote controller is inputted, the first FET Q1 and second FET Q2attempt to rise while fully open (the FETs are fully open during an ONperiod in order to trigger an output quickly), and thus transients suchas an overshoot or undershoot occur. By altering the ON period asdescribed above, the first FET Q1 and second FET Q2 are caused to softstart, enabling a smooth rise without the occurrence of transientsduring the output voltage rise time. The reference symbol 27 in FIG. 1is a constant current circuit.

To describe operations of the present invention using the time chartshown in FIG. 8, when a drive signal (the aforementioned driving signal)is outputted in a cycle T_(A), the ON period T_(a) becomes extremelynarrow during dropping circuit operations and the like, as shown on theright-hand side of the drawing. Then, by ON-OFF controlling the FETs Q1,Q2 in the driving circuits 5, 6 by means of the aforementioned drivesignal, the gate voltage V_(G2) of the second FET Q2 switches to ananalogous opposite phase to the gate voltage V_(G1) of the first FET Q1.At this time, the rise time of the gate voltage V_(G1) of the first FETQ1 is delayed in respect of the rise time of the drive signal by T1, andthe rise time of the gate voltage V_(G2) of the second FET Q2 is delayedin respect of falling of the drive signal by T2. When a typical forwardconverter (ON/ON circuit) is used as the driving circuit of the secondFET Q2, the drain-source voltage V_(DS3) of the third FET Q3 drops at acertain point, as shown in the center of the drawing, but by using thereverse converter 11 (ON-OFF circuit) according to the presentinvention, the voltage can be set in a substantially rectangular-formwave which does not drop, as shown on the right-hand side of thedrawing. The reference symbol I_(D1) in FIG. 7 indicates the draincurrent of the first FET Q1. This is indicated by I_(D) in FIG. 5. V_(T) indicates the primary side and secondary side voltages of thehigh-frequency transformer 3.

According to the first and second phase of the present invention, apartial resonance circuit and a reverse converter are used, and thus thedriving voltage (more specifically, the gate voltage VG2) can beprevented from dropping. Moreover, by providing the driving circuit witha delay element, switching loss can be reduced, and thus a computerpower supply in which efficiency is increased by at least 5% or more (tobetween 70% and 75%) compared to a conventional device using coolingfans can be provided.

According to the third phase of the present invention, a magneticamplifier having a dead angle is provided in the secondary side outputcircuit or a magnetic snubber is provided in the synchronous rectifiercircuit, and thus outflow of the secondary side current can be delayedand the loss of the ZVS (zero voltage switching) function can beprevented.

According to the fourth phase of the present invention, the primary sidewinding end and an earth side end of at least one of said switchingelements are connected in series to two condensers having differingcapacitance, and a diode is connected in parallel to the condenser withthe smaller capacitance, and thus switching loss when the switchingelements are not being driven (OFF) can be reduced, thereby enabling afurther improvement in efficiency.

According to the fifth phase of the present invention, two auxiliarywindings which are different to an output winding provided on thesecondary side are disposed on the secondary side, two synchronousrectifier driving circuits for transferring the output from the primaryside with little loss are connected to the two auxiliary windingsrespectively in a state of differing polarities, and a switching elementfor the two synchronous rectifier driving circuits, which is providedwith an ON-OFF signal synchronously with the secondary voltage of thehigh-frequency transformer, is provided. Thus the switching elements canbe switched ON and OFF smoothly, and since the windings of thetransformer are used, synchronous timing is easy.

According to the sixth phase of the present invention, when an inputvoltage is inputted or an ON signal is inputted from a remotecontroller, the switching elements can be caused to rise smoothlywithout the occurrence of transients during the rise of the outputvoltage.

1. A computer power supply wherein a first switching element and asecond switching element operating with a DC voltage as an input aredisposed on the primary side of a high-frequency transformer, said firstswitching element is connected to one end of a primary side winding ofsaid high-frequency transformer, and said second switching element isconnected to the same end of the primary side winding as the connectionside of said first switching element via a resonance condenser and in astate of differing polarity to said first switching element, saidprimary side winding, resonance condenser, and two switching elementsconstituting a partial resonance circuit, a secondary side outputcircuit for driving a load is connected to the secondary side of saidhigh-frequency transformer via a winding, a first driving circuit and asecond driving circuit having a delay element are provided for drivingand halting said first switching element and second switching element onthe basis of a driving signal by causing the respective phases thereofto differ, and a reverse converter is provided for supplying to theinput portion of one of said driving circuits insulation from the otherof said driving circuits and a reverse input voltage.
 2. The computerpower supply according to claim 1, wherein said reverse converter isdisposed about an iron core such that the primary side winding andsecondary side winding have differing polarities.
 3. The computer powersupply according to claim 1, wherein a magnetic amplifier having a deadangle is provided in said secondary side output circuit or a magneticsnubber is provided in a synchronous rectifier circuit.
 4. The computerpower supply according to claim 1, wherein said primary side winding endand an earth side end of at least one of said switching elements areconnected in series via two condensers having differing capacitance, anda diode is connected in parallel to the condenser with the smallercapacitance.
 5. The computer power supply according to claim 1, whereintwo auxiliary windings, which are different to an output windingprovided on the secondary side of said high-frequency transformer, aredisposed on said secondary side; two synchronous rectifier drivingcircuits for transferring the output from the primary side to said twoauxiliary windings with little loss are connected to the two auxiliarywindings respectively in a state of differing polarities; and switchingelements for said two synchronous rectifier driving circuits areprovided, which are bestowed with an ON-OFF signal synchronously withthe secondary voltage of said high-frequency transformer.
 6. Thecomputer power supply according to claim 1, wherein two resistors fordetermining the ON periods of said first switching element and secondswitching element are connected to a PWM control circuit for outputtingsaid driving signal so as to be parallel when a comparator forcontrolling the ON periods of said first switching element and secondswitching element is ON.